Refrigeration system with loading and unloading control



Nov. 5, 1968 H. SOUMERAI ETAL 3,408,327

REFRIGERATION SYSTEM WITH LOADING AND UNLOADING CONTROL Filed Sept. l9, 1967 2 Sheets-Sheet 1 NOV. 1968 H. SOUMERAI ETAL 3,403,327-

REFRIGERATION SYSTEM WITH LOADING AND UNLOADING CONTROL 2 Sheets-Sheet 2 Filed Sept. 19. 1967 INVENTORS United States Patent ()fice 3,408,827 REFRIGERATION SYSTEM WITH LOADING AND UNLOADING CONTROL Henri Soumerai, West Hartford, Harold W. Moody, Jr.,

Farmington, Clark B. Hamilton, Wethersfield, and James R. Blatt, Coventry, Conn., assignors to Dunham- Bush, Inc., West Hartford, Conn., a corporation of Connecticut I Continuation-impart of application Ser. No. 612,222,

Jan. 27, 1967. This application Sept. 19, 1967, Ser.

No. 668,804 t 8 Claims. (Cl. 62-196) ABSTRACT OF THE DISCLOSURE A refrigeration system is disclosed having a compres sor of the screw type, and a stream of compressed gas and oil mist is used to cool the compressor and the motor. The oil is separated by passing the stream of refrigerant gas and oil through a unit which subjects the oil-laden gas to a thorough oil-separating treatment without restricting the flow of the oil-free gas.

This application is a continuation-in-part of application Ser. No. 612,222, filed Jan. 27, 1967, and covering the refrigeration system of the illustrative embodiment of the present invention. This application is related to application Ser. No. 666,372 filed Sept. 8, 1967, which is directed to the details of structure and mode of operation involved in the separation of the oil which is entrained in the stream of compressed refrigerant gas. The present application is directed to the control of the loading and unloading of the compressor.

This invention relates to refrigeration, and more in particular to a refrigeration system wherein the compressor is of the screw type.

This invention is particularly directed to a system and method for unloading and loading a screw compressor, utilizing the compressed gas and the oil as the control fluids.

An object of this invention is to provide an improved means for controlling the loading and unloading of a screw compressor. A further object is to provide an improved system and method for controlling the loading and unloading of the compressor of a refrigeration system wherein oil is used as a lubricating and cooling medium. A further object is to provide accurate and dependable control for screw compressors in refrigeration systems Another object is to provide for the above under varying loads and extreme conditions of use. These and other objects will be in part obvious and in part pointed out below.

In the drawings:

FIGURE 1 is a schematic representation of one embodiment of the invention;

FIGURE 2 is an enlarged vertical section of the lower left-hand portion of the evaporator-chiller shown at the bottom of FIGURE 1;

FIGURE 3 is a sectional view of the control unit shown in the upper right-hand portion of FIGURE 1; and,

FIGURE 4 is a sectional view on the line 44 of FIG- URE 3.

Referring to FIGURE 1 of the drawings, a refrigeration system 2 includes: a screw compressor 4 having an unloader 5 and driven by an electric motor 6; an oil separator 8; a refrigerant discharge line 10; a water-cooled condenser 12; a liquid refrigerant line 14 extending to a heat exchanger 16 which acts as a superheater unit; a liquid refrigerant dryer-filter 18; a liquid supply control 3,408,827 Patented Nov. 5, 1968 assembly 20 through which the liquid refrigerant flows to a distributor header 22 for a plurality of liquid distributor tubes 24; an evaporator-chiller 26 having a refrigerant inlet header 28 and a refrigerant outlet tube plate 30; and, a gas refrigerant return line 32 through which the gas refrigerant returns to compressor 4.

The system also includes an oil circulatingsystem including the following in series: an oil sump 34; an oil pump 36 driven by an electric motor 37; an oil cooler 38 through which water flows from a water inlet 40 to a water outlet 42 and which cools the oil flowing from the pump and, an oil filter 44. An oil supply line 46 delivers oil under controlled pressure through distributor lines 48 to the motor bearings and through lines 52 and 54 and 56 to compressor 4. Oil is also delivered from line 46 through a line 58 to the unloader 5, and through a line 59 to a load control unit 60.

Chiller 26 has refrigerant tubes which are supported within the shell between their ends and are mounted at their ends in tube plates 82 and 84, respectively (see also FIGURE 2). Mounted on tube plate 82 is an orifice plate 86 which is held in place beneath a header 88. Orifice plate 86 has a plurality of small round openings or orifices 90 which are so positioned that one of them is in axial alignment with the end of each of the evaporator tubes 80. Header 88 has a plurality of ribs 92 which rest against orifice plate 86 and divide the area of the orifice plate into a number of header chambers 94, each of which receives liquid refrigerant through one of the distributor tubes 24. The pattern of ribs 92 is such that substantially the same number of orifices 90 is in each of the header chambers 94. Hence, the refrigerant supplied to each of tubes 24 is delivered through one of the headers and its orifices 90 to a specific group of evaporator tubes 80. Each of the orifices 90 acts as an expansion unit to provide the desired pressure drop, so that each of the evaporator tubes is in effect a separate evaporator. Also, substantially the same amount of the refrigerant flows to each chamber 94, and it is then distributed substantially evenly to .a relatively small number of evaporator tubes. Hence, a highly efficient and dependable arrangement is provided for distributing the refrigerant substantially equally to all of the evaporator tubes.

As indicated above, the discharge ends of the evaporator tubes are supported in a tube plate 84, and the tubes open into the shell 96 of the heat exchanger 16. Water or other liquid to be cooled flows to and from shell 98 through a pair of lines 100 and 102. The refrigerant gas flowing through shell 96 of heat exchanger 16 cools the liquid refrigerant in coil 104, and the gas then flows through a filter 106 and through line 32 back to compressor 4. Positioned in heat exchange relationship with the returning refrigerant gas are two control bulbs 108 and 110 which control liquid supply or regulator valves 112 and 114, respectively through controllers 116 and 118. Valves 112 and 114 are in parallel. Valve 114 is fully closed at low loads, for example, below 35% of full load, and valve 112 determines the supply of liquid refrigerant to header 22 below 35% of full load. At loads above 35% of full load valve 112 is fully open and the control is exerted by valve 114.

During operation, the dense high-pressure oil-gas mixture is discharged from compressor 4 into a chamber at 62 and thence through the motor where it is discharged axially into the oil separator 8. This gas-oil mixture uniformly blankets and cools the stator and rotor of the motor, and the motor also serves as a first-stage oil separator and removes, by centrifugal action, the bulk of the oil entrained in the gas. It has been found that something of the order of 95% of the oil is removed by the motor, and the oil accumulates in thebottom of the housh shit gas flows pasta checkvalve .75 to line 1 0.

As indicated above, unloader .5 controls the operation of the compressor so that it compresses the amount of refrigerant required for the load atall times. Accordingly, compressor 4 has acapacity control slide valve 120 which isstiow'ri in the full-load position wherein it forms a portion of the compressor-rotor casing 122. Slide valve 120 is mounted to slide to the" left from the position shown to thereby expose an opening in the bottom of the rotorcasing through which the suction gas can pass back from the central portion of the compressor to the suction inlet. In this way the amount of gas pumped is reduced.

Slide valve 120,is connected through an operated spindle 124 to a piston 126 which is' slidable in a cylinder 128. Piston 126 is moved to the left from the position shown lay-supplying oil at a controlled pressure'to the chamber 130 in the cylinder at the rightof the piston. Cylinder 128 is open at its left-hand end to the suction pressure of'the compressor". Hence, when oil is supplied to chamber 130 at'a pressure greater than the discharge pressure, piston 126- is moved to the left; and, when the pressure of the oil in chamber 130 is less than the discharge pressure, piston 126 moves to'the right. Oil supply line 58 is connected to chamber 130 through a shutoff valve 132 and a line 134. Hence, when valve 132 is open the oil at the full pressure in lines 46 and 58 is supplied to chamber 130. Also, a flow circuit is provided inparallel withvalve 132 by line 59 and a restrictor valve 136 and a shut-off valve 138. Hence, when valve 132 is closed and valve 138 is opened, the oil at the pressure of line 46 flows through line 59, r'estrictor 136, valve 138 and line 134 to chamber 130. However, restrictor 136 limits the rate of. fiow sothat piston 126 is moved at a reduced but controlled rate, whereas when valve 132 is open the piston movesat a rapid rate. This permits unloading rapidly by opening valve 132, orunloading at a slower rateby opening valve 138.

An additional control circuit is provided by a shut-off valve 140 and a restrictor 142 in a line 144 which extends between the suction inlet of the compressor housing and chamber 130. Hence, when valve 140 is open the oil in chamber 130 is free to flow through line 134, restrictor 142, line 144, and valve 140 to the compressor casing. As indicated above, when the compressor is operating, the pressure of the compressed gas at the discharge side of the compressor urges sliding valve 120 toward its full-load position. Hence, when valve 140 is open, the pressure equalizes onthe two sides of the piston because of. the fiow'of oil from chamber 130, and the discharge pressure acting on slide valve 120 moves the slide and piston 126 back to the right. Restrictor 142 controls therate of flow ofoil from chamber 130 andtherefore controls the rate of movement of the piston froma partialload position to the full-load position.

The oil pressure in line 46 is controlled by a control unit 146 which has a valve 148 in a line 150 extending new w s thrgugha line 35 to gil sllfllp. 34......

Tilt; pfiniugnQfevalve .140 when thecompressor is.par: daily or completely unloaded will fully load it at a controlled rate.

The present invention provides for the accuate and dependable control of the movement of the unloader piston and slide.- Mounted upon and closingthe right-hand end of cylinder 128 isa control'unit 200 having a casing 201 which is'clamped'in place by'a plurality ofstud bolts 202. Mounted on piston-126 is'a cable bracket 204 to which is secured one en'dof a cable 206.The other end of cable 206 is attached to a cylindrical reel 208, and the .cable is wound from thatend around the reel. Reel 208 is rotatablemounted upon a fixed vertical spindle210,

' which is mounted in the bottom wall 211 of-casing 201,

from line 46 to sump 34. -A control line 152 extends from unit 146 to the discharge chamber 62 ofthe compressor so that unit 146 is responsive tothe compressor discharge pressure. Unit 146 and its valve 148 act as a relief valve to maintain a pressure in' line 46 which is a predetermined amount above the pressure in chamber 62. Illustratively, when the compressed gas pressure in chamber 62 is 200 pounds per Square inch, the pressure in line 46 is 240 poundsper square inch. Hence, the oil delivered to the compressor through the various lines 48, 52, 54 and 56, and through lines 58v and 59 to theunloader is maintained at a predetermined value above the compressor discharge pressure. This insures a proper andadequate supply of oil to the motor bearings and to the compressor. It also insures that the unloader will operate properly. The opening of valve 132 when the compressor is partially or fully loaded will unload it at a rapid rate.

and encloses a flat coil spring (see FIGURE 4) 212 which is connected at its inner end to the fixed spindle and at its outer end to the reeL-Spring 212 is wound to provide tension opposing the turning of the reel in the direction to unwind cable'206. Hence, as piston 126 moves back and forth during the loading and unloading of the compressor, cable 206 is wound and unwound on the reel; and, that turning movement of the reel is used to indicate the position of the piston and slide 120. Stated differently, the movement of piston 126 turns reel 208,and the relative arcuate position of the reel always has a definite relationship to the relative loading condition of the: compressor. Rotatably mounted in a pair of bearings 214 above spindle 210, and in axial alignment with the spindle, is a drive shaft 216 upon which is clamped a crank'arm 218. Crank arm 218 is mechanically connected by a pin 220 to turn with reel 208. Hence, shaft 216 also moves with and has an arcuate position which is directly related to the relative position of the piston and slide. Mounted upon the upper end of shaft 216 is the moving element of a unit 222 which, in turn, is a portion of a unit 224.

Shaft 216 also carries a bevel gear 226 which meshes with a gear 228 (see FIGURE 4) keyed to a shaft 230 which is mounted in a bearing in a bracket 232. Shaft 230 extends into the casing of a variable resistor 234 andis connected to the resistor slide (not shown). Hence, the

loading and unloading of the compressor by the movement of piston 126 turns shaft 216 which extends "to unit 224, and also turns shaft 230 and adjusts the slide on resistor 234. p

The loading and unloading of the compressor is controlled by a control unit to which resistor 234' is connected, and is a Honeywell Solid-State Control Unit, Model W-751A, manufactured by Honeywell, Inc. of Minneapolis, Minnesota, and explained in that companys bulletin Form No; 95-7026, dated April 1967. That control unit senses the temperature of the water leaving the chiller by means of a temperature-responsive electrical resistance unit or sensor. The sensor is in one leg of a bridge circuit, and the bridge circuit-also includes a rheostat which is an adjustable temperature control unit for the system. The position of the slide on that rheostat is calibrated in terms of temperature, and a change in the temperature adjustment changes the effect in the bridge circuit of that rheostat. When the' temperature control unit is set at a particular temperature, the bridge is in balance only when the sensor is at that temperature. When the sensor temperature is too high, the bridge initiates a control action to move the slide valve 120 toward unloading the compressor; and when that temperature is too unload, respectively. The movement of the slide valve.

produces a feed-back, to-the control unit by the movement of the slide on resistor 234. I

It has been pointed out abovethat the heavy mixture of compressed gas and oil mist provides a very satisfactory cooling of the motor. The oil mist produces a scrubbing action which improves the heat exchange factor and increases the cooling of the motor. The oil which is sup plied to the compressor may contain some refrigerant and that refrigerant tends to flash and to aid in the cooling effect of the oil. It is thus seen that the refrigerant and the oil are circulated through separate cycles, but that inter-relationship is maintained which provides an improved mode of operation. Pump 36 is started prior to the starting of motor 6 so that the oil pressure builds up and provides oil for the motor and compressor, and the desired oil pressure is provided for the unloader. The controls also provide automatic unloading at start-up.

A hot gas bypass line 11 is connected between the gas refrigerant discharge line 10 and the liquid supply line 21 through which liquid refrigerant flows from valves 112 and 114 to distributor header 22. Line 11 includes a cutoff solenoid valve 23 and a restrictor 15. When desirable, valve 23 is opened to supply hot gas under the control of restrictor 15 to prevent stratification of the liquid phase and unstable operation of the refrigerant controls. For example, at low loads, there is a tendency for the liquid refrigerant to flow only through certain of the evaporator tubes 80. That condition is corrected by opening solenoid valve 23 so that hot refrigerant gas flows with the liquid refrigerant through header 22 and through the distributor lines to the various chambers 94 and through tubes 80. The amount of hot gas is controlled by restrictor valve 15 and is such as to insure continuous flow of the refrigerant through the evaporator tubes.

The opening of solenoid valve 23 is under the control of unit 224 wherein a cam 240 is rotated to close a normally-open switch 242. Switch 242 is connected at one side to one power line 243 of an electric power source, and at the other side, through a line 244 to the solenoid of valve 23. The other side of the valve solenoid is connected to the other power line 246 so that the closing of switch 242 energizes the solenoid and opens the valve. During operation, when the load on the compressor decreases to a predetermined value, as indicated by the turning of shaft 216 (FIGURE 3) to a predetermined position, cam 240 (FIGURE 1) closes switch 242 so that hot gas is delivered to line 21 at the rate determined by the adjustment of valve 15. That rate is suflicient to insure the desired rate of flow of liquid refrigerant through the evaporator tubes. Cam 240 is also adjustable to permit the opening of valve 23 at one position of slide valve 120 during unloading of the compressor and the closing of the valve at another position of the slide valve during the loading of the compressor. The opening and closing of the valve is regulated depending upon the conditions of operation of the system. Illustratively, for one mode of operation, during the starting of the compressor, valve 23 is open until slide valve 120 has moved from its fully unloaded position approximately of its travel toward its fully loaded position, so that the compressor is operating in the range of to of full load, at which time the valve closes. However, during unloading, valve 23 remains closed until the slide valve reaches its position where the load has been reduced to the order of 10% of full load.

It has been indicated above that valve 114 is closed at low loads, for example at loads below 35% full load. The closing of valve 114 is effected by deenergizing its solenoid under the control of unit 224. Unit 224 has a cam 260, which is rotated by shaft 216 (FIGURE 2) to open a normally-closed switch 262 when valve 114 is to be closed. Switch 262 is connected at one side to a power line 264 and at the other side, through a line 266 to the valve solenoid. The other side of the valve solenoid is connected to the other power line 268. Hence, when shaft 216 is turned to the position which it reaches when valve 114 is to be closed, cam 260 opens switch 262 and that closes the valve. Valve 112 then determines the amount of liquid refrigerant which is supplied to header 22. Cam 260 is adjustable, and the cam may be adjusted so that valve 114 opens at a different loading condition than at which it closes. For example, during start up and loading of the compressor, valve 114 may open when the slide 6 1 1 valve is moved 33% of its travel distance from its fully unloaded position toward as fully loaded position, whereas it may close during unloading when the slide valve is moved back to a position which is 26% of that travel distance from the fully unloaded position. In terms of compressor loading, those percentages represent approximately 45% and 35%, respectively, of full load.

What is claimed is: I

1. In a refrigeration system, the combination of, a screw-type compressor having an unloader slide which is moved from and to a full-load position to control the operating capacity, means constituting with said compressor a complete refrigeration system including an evaporator, operating means to move said unloader slide throughout its operating range, fluid supply means to supply fluid under pressure to operate said operating means, fluid control means to control the supply of said fluid under pressure to said supply means to maintain the desired load condition on said compressor, liquid refrigerant supply means to control the supply of refrigerant to said evaporator and including a plurality of restrictor means in parallel, and auxiliary control means to stop the flow of refrigerant through one of said restrictor means at compressor loads below a predetermined value.

2. In a refrigeration system, the combination of, a screw-type compressor having an unloader slide which is moved from and to a full-load position to control the operating capacity, means constituting with said compressor a complete refrigeration system including an evaporator and restrictor means through which liquid refrigerant is supplied to said evaporator, operating means to move said unloader slide throughout its operating range, fluid supply means to supply fluid under pressure to operate said operating means, fluid control means to control the supply of said fluid under pressure to said control means to maintain the desired load condition on said compressor, hot gas supply means to supply hot gas at a controlled rate from said compressor to the stream of liquid flowing from said restrictor means to said evaporator, and control means for said hot gas supply means which is responsive to the load condition on said compressor and which shuts off said hot gas supply throughout the load condition between the full load con-- dition and a predetermined partial load condition.

3. A refrigeration system as described in claim 2 wherein said evaporator has substantially horizontal refrigerant tubes, and wherein said restrictor means comprises a plurality of restrictors in parallel, and which includes control means to stop the flow of liquid refrigerant through one of said restrictors at load conditions on the compressor below a predetermined value.

4. A refrigeration system as described in claim 2 wherein said control means for said hot gas supply means includes an electric switch and cam means to operate said electric switch and mechanically connected to be moved by the movement of said unloader slide.

5. A refrigeration system as described in claim 2 wherein said evaporator is a liquid chiller unit, and wherein said restrictor means varies the flow of liquid refrigerant to said evaporator in accordance with the temperature of the refrigerant gas flowing from the evaporator.

6. In a system of the character described, the combination of, a screw-type compressor having an unloader slide which is moved from and to a full-load position to control the operating capacity, operating means to move said unloader slide throughout its operating range and comprising a cylinder and piston assembly operatively connected to said unloader slide, oil supply means to provide oil under pressure to operate said cylinder and piston assembly, a control unit mounted upon said piston and cylinder assembly and including cam means and switch means operated thereby, and means attached to be moved with said unloader slide and connected to move said cam means.

comprises fa cord "itidohedfat "orig 'tq' fthg pistop o f said as sembly, arrd wlherein saidklonfrol unif'includgs a spring andljdn'rnisscmbly. which is-a'dapt ed to windusaid cord thereon to thereby translate the-longitudinal movement of said end of said cord into arcuate movementof said drum.v .1 M

-8. Apparatus as .described-in claim 7: wherein 'said control meansincludes a rhe'ostat andmeans adjusting MEYER PERLIN; Primar y-E J caminer. v 

